Low-k dielectric insulating materials are used in the fabrication of semiconductor devices as a means to reduce resistance capacitance (RC) delay time which inhibits device performance speed and increases power consumption. Low-k dielectrics are used, for example, as inter-metal dielectrics (IMD) and inter-layer dielectrics (ILD) between conductive traces to improve semiconductor device performance as such devices and circuits therein continue to shrink in size with advances in fabrication technology. Low-K materials are generally considered those with dielectric constants less than 3.
Low-k dielectric films may be deposited on a wafer by various CVD (chemical vapor deposition) or spin-on processes. These dielectric materials are cured after deposition by irradiation with UV light for many reasons including improving and/or restoring the physical properties to the film material such as increasing elastic modulus or hardness to improve mechanical strength for higher packaging yields and/or to better withstand post-film deposition processes such as etching, chemical cleaning, CMP (chemical mechanical polishing), wire bonding, etc. In addition, UV curing is used to repair damage to the film caused by chemicals such as fluorine and nitrogen, and to restore the low k properties of the film which may increase during some post-film deposition processes.
During UV curing of low-k dielectric films, it is desirable to maintain uniform UV curing intensity over the entire surface of the wafer to avoid problems such as film shrinkage at portions of the wafer that may be disproportionately exposed to greater levels of irradiation which may result in variability in device performance. Existing UV curing apparatus arrangements sometimes result in higher localized UV irradiation intensity regions on the wafer, which may occur at the center of the wafer and/or in one or more other isolated regions. The differential wafer irradiation profile may be attributed to the UV lamp arrangement and/or curing process used. As wafer sizes move from 300 mm to 450 mm wafers, the non-uniformity problems can be expected to worsen.
Improved UV curing systems and methods are desired.
All drawings are schematic and are not drawn to scale.